Lubricating oil composition for refrigerating machine

ABSTRACT

A lubricating oil composition for refrigerator is formed by adding an organic compound that includes a double bond in the molecule such as α-olefin or conjugated diene to a base oil. Capable of being stably used for a long time in the presence of oxygen, the lubricating oil composition for refrigerator according to the invention is suitable for an open-type car air-conditioner, an electric driven car air-conditioner, a gas heat pump, an air conditioning device, a refrigerator, a vending machine, a showcase, various hot-water supply systems or a heating/cooling system.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition forrefrigerator used in a compression freezer(s) of various freezer fields.

BACKGROUND ART

In general, a compression freezer includes a compressor, a condenser, anexpansion valve and an evaporator. Within an enclosed system of thecompression freezer, a liquid mixture of a refrigerant and lubricatingoil is circulated. Examples of a refrigerant conventionally used in manyof such compression freezers include dichlorodifluoromethane (R12) andchlorodifluoromethane (R22). Examples of the lubricating oilconventionally used therein are a variety of mineral oil and syntheticoil.

However, chlorofluorocarbon such as R12 and R22 mentioned above maybring about an environmental pollution such as destruction of thestratospheric ozone layer, a use of which has been more strictlyregulated on a global scale in recent years. Thus, a hydrogen-containingchlorofluorocarbon compound such as hydrofluorocarbon orhydrochlorofluorocarbon is attracting more and more attentions as a newrefrigerant. Such a hydrogen-containing chlorofluorocarbon compound,especially hydrofluorocarbon represented by R134a, is a preferablerefrigerant for compression freezers not only because the compound doesnot destroy the ozone layer but also because the compound can be used inconventional freezers in place of R12 and the like with little change inconfigurations of freezers from those of the conventional freezers(e.g., see Patent Document 1).

Since hydrofluorocarbon may bring about an impact on the environment interms of global warming, a so-called natural refrigerant such as carbondioxide or ammonia is also attracting more and more attentions as analternative refrigerant that is more suitable for environmentalprotection. Refrigerator oil using such a natural refrigerant has beenalso proposed (e.g., see Patent Document 2). In addition, a refrigeranthaving a specific polar structure in its molecule such as an unsaturatedfluorohydrocarbon compound, a fluoroether compound, a fluoroalcoholcompound or a fluoroketone compound has been found to have lower globalwarming potential (e.g., see Patent Document 3 and Patent Document 4).

Patent Document 1: JP-A-10-008078

Patent Document 2: JP-2000-96075

Patent Document 3: JP-T-2006-503961

Patent Document 4: JP-T-07-507342

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, the refrigerator oil disclosed in Patent Document 1 or 2 is notnecessarily sufficiently superior in terms of energy saving. Forinstance, even when the refrigerator oil is used in a freezer such as anautomobile air conditioner or an electric refrigerator, friction betweenan aluminum product and a steel product of the freezer remains large,which is problematic in terms of energy saving. In addition, since agreat variety of refrigerants are in use as set forth above, it has beendifficult to provide a single refrigerant oil that can be used withthose refrigerants. Furthermore, although it is necessary that thelubricating oil for refrigerator utilized with the refrigerant disclosedin Patent Document 3 or 4 has excellent stability as well as excellentcompatibility with the refrigerant, lubricating oil having sufficientstability has not been provided yet.

An object of the present invention is to provide a lubricating oilcomposition for refrigerator that provides excellent stability whenimplemented as refrigerator oil utilized in freezers which employ avariety of refrigerants such as an unsaturated fluorohydrocarboncompound that have a low global warming potential and are employed for aconventional automobile air conditioning system.

Means for Solving the Problems

In order to solve the above-mentioned problems, according to an aspectof the invention, lubricating oil compositions for refrigerator asfollows are provided:

(1) a lubricating oil composition for refrigerator, comprising: a baseoil; and an additive added to the base oil, in which the additive is anorganic compound comprising a double bond in its molecule;

(2) the above-described lubricating oil composition for refrigerator, inwhich the organic compound is an unsaturated aliphatic compound;

(3) the above-described lubricating oil composition for refrigerator, inwhich the unsaturated aliphatic compound is α-olefin;

(4) the above-described lubricating oil composition for refrigerator, inwhich the unsaturated aliphatic compound comprises a conjugated doublebond;

(5) the above-described lubricating oil composition for refrigerator, inwhich the organic compound is a compound selected from terpenes thatcomprise a double bond;

(6) the above-described lubricating oil composition for refrigerator, inwhich the lubricating oil composition for refrigerator is used for arefrigerant containing: at least one of fluorine-containing organiccompounds selected from the compounds represented by the followingmolecular formula (A); or a combination of the fluorine-containingorganic compound and saturated fluorohydrocarbon compound,

C_(p)O_(q)F_(r)R_(s)  (A)

where: R represents a Cl, Br, I or hydrogen atom, p is an integer in arange of 1 to 6, q is an integer in a range of 0 to 2, r is an integerin a range of 1 to 14, and s is an integer in a range of 0 to 13; and ifq is 0, p is in a range of 2 to 6, and the molecule includes at leastone carbon-carbon unsaturated bond;

(7) the above-described lubricating oil composition for refrigerator, inwhich the compound represented by the molecular formula (A) is acompound represented by at least one of molecular formulae C₃HF₅,C₃H₂F₄, and C₃H₃F₃,

(8) the above-described lubricating oil composition for refrigerator, inwhich the base oil is mineral oil and/or synthetic base oil, and thesynthetic base oil is at least one compound selected from a groupconsisting of alkyl benzene, alkyl naphthalene, poly-α-olefin, polyvinylether, polyalkylene glycol, polycarbonate, polyol ester and anether-base compound represented by a formula (1) as follows,

Ra-[(ORb)n—(B)—(ORc)k]x-Rd  (1)

where: Ra and Rd each represent a hydrogen atom, an alkyl group having 1to 10 carbon atoms, an acyl group having 2 to 10 carbon atoms or ahydrocarbon group having 2 to 6 bonding sites and 1 to 10 carbon atoms;Rb and Rc each represent an alkylene group having 2 to 4 carbon atoms; nand k each represent an integer in a range of 0 to 20; x represents aninteger in a range of 1 to 6; (B) represents a polymerization sitecontaining 3 or more monomer units each represented by a formula (2) asfollows,

where: R⁴, R⁵ and R⁶ each represent a hydrogen atom or a hydrocarbongroup having 1 to 8 carbon atoms, R⁴, R⁵ and R⁶ being allowed to bemutually the same or different; R⁷ represents a divalent hydrocarbongroup having 1 to 10 carbon atoms or divalent ether-bondedoxygen-containing hydrocarbon group having 2 to 20 carbon atoms; R⁸represents a hydrogen atom, a hydrocarbon group having 1 to 20 carbonatoms; m represents a number whose average value is in a range of 0 to10; when m is plural, plural m may be mutually the same or different pereach unit; R⁴ to R⁸ each may be mutually the same or different per eachunit; when R⁷O is plural, plural R⁷O may be mutually the same ordifferent; and when both k and n in the formula (1) are 0, m is aninteger of 1 or larger in the formula (2);

(9) the above-described lubricating oil composition for refrigerator, inwhich the base oil is further added with at least one additive selectedfrom a group consisting of an extreme pressure agent, an oiliness agent,an antioxidant, an acid scavenger, a metal deactivator and anantifoaming agent;

(10) the above-described lubricating oil composition for refrigerator,in which a slide portion of the refrigerator is made of engineeringplastic or includes an organic coating layer or an inorganic coatinglayer;

(11) the above-described lubricating oil composition for refrigerator,in which the organic coating layer is a coating layer ofpolytetrafluoroethylene, a coating layer of polyimide, a coating layerof polyamide-imide or a thermosetting insulating layer formed with useof a resin paint containing: a resin base material made ofpolyhydroxyether resin and polysulfone-base resin; and a cross-linker;

(12) the above-described lubricating oil composition for refrigerator,in which the inorganic coating layer is a graphite layer, a diamond-likecarbon layer, a tin layer, a chromium layer, a nickel layer, of amolybdenum layer;

(13) the above-described lubricating oil composition for refrigerator,the lubricating oil composition for refrigerator is used in an open-typecar air-conditioner, an electric driven car air-conditioner, a gas heatpump, an air conditioning device, a refrigerator, a vending machine, ashowcase, various hot-water supply systems or a heating/cooling system;and

(14) the above-described lubricating oil composition for refrigerator,in which a water content within the system is 500 ppm by mass or lesswhile a residual air partial pressure is 13 kPa or less.

The lubricating oil composition for refrigerator according to an aspectof the invention includes an additive in the form of an organic compoundhaving a double bond in the molecule thereof added to a base oil.Accordingly, a small amount of oxygen remaining in the freezer systemcan be scavenged, thereby preventing oxygen from reacting with therefrigerant. Therefore, the lubricating oil composition for refrigeratoraccording to the aspect of the invention can be stably used for a longtime.

The freezer lubricating oil composition according to the aspect of theinvention is suitable for use in an application that employs anunsaturated chlorofluorocarbon refrigerant reactive particularly withoxygen such as an automobile air conditioner, an automobile airconditioner with electric motor driven compressor, a gas heat pump, anair conditioner, a refrigerator, a vending machine, a showcase,hot-water supply systems, or a heating and refrigerating system.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment for implementing the present invention will bedescribed below.

A lubricating oil composition for refrigerator according to theinvention is formed by adding an organic compound having double bond inthe molecules to a base oil.

The base oil may be mineral oil or synthetic base oil. Examples ofpreferable synthetic base oil include at least one synthetic base oilselected from a group consisting of alkyl benzene, alkyl naphthalene,poly-α-olefin, polyvinyl ether, polyalkylene glycol, polycarbonate,polyol ester, and an ether compound represented by the formula (2).

First of all, the base oil will be described below.

1. Mineral Oil

The mineral oil is preferably highly-refined mineral oil, examples ofwhich are: refined oil provided by refining oil fractions in accordancewith an ordinary method; deeply-dewaxed oil provided by deeply dewaxingthe refined oil fractions; and hydrotreated oil provided byhydrotreating the oil fractions, the oil fractions being provided byatmospherically distilling paraffin-base crude oil, intermediate-basecrude oil or naphthene-base crude oil or by vacuum-distilling theresidual oil of the atmospherically-distilled oil. The method ofrefining is not particularly limited but various methods may beemployed.

In general, a treatment such as (a) hydrotreating, (b) dewaxing(solvent-dewaxing or hydrodewaxing), (c) solvent-extracting, (d)alkali-distilling or sulfate-cleaning or (e) clay-treating is singularlyperformed, or plural methods thereof are combinationally performed in asuitable order. In addition, performing the same treatment plural timesis also effective. For instance, the oil fractions may experiencehydrotreating, the oil fractions may initially experience hydrotreatingand subsequently alkali-distilling or sulfate-cleaning, the oilfractions may initially experience hydrotreating and subsequentlydewaxing, the oil fractions may initially experience solvent-extractingand subsequently hydrotreating, the oil fractions may experiencehydrotreating twice or three times, the oil fractions may initiallyexperience hydrotreating twice or three times and subsequentlyalkali-distilling or sulfate-cleaning, or the oil fractions mayinitially experience the above-described treatment(s) and subsequentlydewaxing again (i.e., deep dewaxing). Among the above-described methods,the mineral oil provided by deep dewaxing is preferable for thehighly-refined mineral oil used as the base oil in the invention becausesuch mineral oil is excellent in low-temperature fluidity and free fromwax precipitation at low temperatures. According to the deep dewaxing,the oil fractions are solvent-dewaxed under severe conditions or the oilfractions are catalytic-dewaxed using a zeolite catalyst.

When the polyvinyl ether-base compound(s) is used as the base oil of therefrigerator oil composition according to the invention, its kinematicviscosity at 40 degrees C. is preferably 1 to 400 mm²/s, more preferably5 to 250 mm²/s.

2. Alkyl Benzene

Examples of the alkyl benzene are any alkyl benzene usable forrefrigerator oil, among which alkyl benzene having high viscosity ispreferably used for the invention. Although there is a variety of suchhighly-viscous alkyl benzene, alkyl benzene whose alkyl group has 20 ormore carbon atoms in total (or alkyl benzene whose plurality of alkylgroups have 20 or more carbon atoms in sum total) such as monoalkylbenzene, dialkyl benzene or trialkyl benzene is preferable. Alkylbenzene having two or more alkyl groups in which 20 or more carbon atomsare contained in sum total (e.g., dialkyl benzene) is more preferablyused in view of thermal stability. As long as kinematic viscosity of thehighly-viscous alkyl benzene is within the above-described range, thehighly-viscous alkyl benzene may be singularly used or two or more ofthe above examples may be mixed to be used.

When the polyvinyl ether-base compound(s) is used as the base oil of therefrigerator oil composition according to the invention, its kinematicviscosity at 40 degrees C. is preferably 1 to 400 mm²/s, more preferably5 to 250 mm²/s.

3. Alkyl Naphthalene

A preferable example of the alkyl naphthalene is alkyl naphthalene whosenaphthalene ring is bonded with two or three alkyl groups. Particularly,alkyl naphthalene having 20 or more carbon atoms in total is morepreferable in view of thermal stability. In the invention, the alkylnaphthalene may be singularly used or a mixture thereof may be used.

When the polyvinyl ether-base compound(s) is used as the base oil of therefrigerator oil composition according to the invention, its kinematicviscosity at 40 degrees C. is preferably 1 to 400 mm²/s, more preferably5 to 250 mm²/s.

4 Poly-α-Olefin

Although there is a variety of usable poly-α-olefin, the poly-α-olefinis typically an α-olefin polymer having 8 to 18 carbon atoms. Thepoly-α-olefin polymer is preferably a 1-dodecene polymer, a 1-decenepolymer or a 1-octene polymer in view of thermal stability, sealability,lubricity and the like. In the invention, hydrotreated poly-α-olefin ispreferably used as the poly-α-olefin in view of thermal stability. Thepoly-α-olefin may be singularly used or a mixture thereof or a polymerof α-olefin mixture may be used.

When the polyvinyl ether-base compound(s) is used as the base oil of therefrigerator oil composition according to the invention, its kinematicviscosity at 40 degrees C. is preferably 1 to 400 mm²/s, more preferably5 to 250 mm²/s.

5 Polyvinyl Ether

Examples of the polyvinyl ether used as the base oil are a compoundprepared by polymerizing vinyl ether monomer (hereinafter called aspolyvinyl ether I), a compound prepared by copolymerizing vinyl ethermonomer and hydrocarbon monomer having olefin double-bond(s)(hereinafter called as polyvinyl ether copolymer II), and a copolymer ofpolyvinyl ether and alkylene glycol, polyalkylene glycol or monoetherthereof (hereinafter called as polyvinyl ether copolymer III).

Examples of vinyl ether monomer used as the material of the polyvinylether I are vinyl methyl ether, vinyl ethyl ether, vinyl-n-propyl ether,vinyl isopropyl ether, vinyl-n-butyl ether, vinyl-isobutyl ether,vinyl-sec-butyl ether, vinyl-tert-butyl ether, vinyl-n-pentyl ether,vinyl-n-hexyl ether, vinyl-2-methoxyethyl ether, vinyl-2-ethoxyethylether, vinyl-2-methoxy-1-methylethyl ether, vinyl-2-methoxy-propylether, vinyl-3,6-dioxaheptyl ether, vinyl-3,6,9-trioxadecyl ether,vinyl-1,4-dimethyl-3,6-dioxaheptyl ether,vinyl-1,4,7-trimethyl-3,6,9-trioxadecyl ether, vinyl-2,6-dioxa-4-heptylether, vinyl-2,6,9-trioxa-4-decyl ether, 1-methoxypropene,1-ethoxypropene, 1-n-propoxypropene, 1-isopropoxypropene,1-n-butoxypropene, 1-isobutoxypropene, 1-sec-butoxypropene,1-tert-butoxypropene, 2-methoxypropene, 2-ethoxypropene,2-n-propoxypropene, 2-isopropoxypropene, 2-n-butoxypropene,2-isobutoxypropene, 2-sec-butoxypropene, 2-tert-butoxypropene,1-methoxy-1-butene, 1-ethoxy-1-butene, 1-n-propoxy-1-butene,1-isopropoxy-1-butene, 1-n-butoxy-1-butene, 1-isobutoxy-1-butene,1-sec-butoxy-1-butene, 1-tert-butoxy-1-butene, 2-methoxy-1-butene,2-ethoxy-1-butene, 2-n-propoxy-1-butene, 2-isopropoxy-1-butene,2-n-butoxy-1-butene, 2-isobutoxy-1-butene, 2-sec-butoxy-1-butene,2-tert-butoxy-1-butene, 2-methoxy-2-butene, 2-ethoxy-2-butene,2-n-propoxy-2-butene, 2-isopropoxy-2-butene, 2-n-butoxy-2-butene,2-isobutoxy-2-butene, 2-sec-butoxy-2-butene, 2-tert-butoxy-2-butene andthe like. The above vinyl ether-base monomers can be manufactured by aknown method.

One of the above vinyl ether monomers may be singularly used or acombination of two or more thereof may be used.

The vinyl ether monomers listed above each may be also used as thematerial for the polyvinyl ether copolymer II. One of the above vinylether monomers may be singularly used or a combination of two or morethereof may be used.

Examples of the hydrocarbon monomer having olefin double-bond(s), whichis the other material of the polyvinyl ether copolymer II, are ethylene,propylene, butenes, pentenes, hexenes, heptenes, octenes, diisobutylene,triisobutylene, styrene, α-methylstyrene, alkyl-substituted styrenes andthe like.

One of the above hydrocarbon monomers having olefin double-bond(s) maybe singularly used or a combination of two or more thereof may be used.The polyvinyl ether copolymer II may be a block copolymer or a randomcopolymer.

The polyvinyl ether I and the polyvinyl ether copolymer II can bemanufactured exemplarily by the following method.

At the initial stage of the polymerization, a compound prepared bycombining Bronsted acids, Lewis acids or organometallic compounds withwater, alcohols, phenols, acetals or an adduct of vinyl ethers and acarboxylic acid may be used. Examples of the Bronsted acids arehydrofluoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid,nitric acid, sulfuric acid, trichloroacetic acid, trifluoroacetic acidand the like. Examples of the Lewis acids are boron trifluoride,aluminum trichloride, aluminum tribromide, tin tetrachloride, zincdichloride, ferric chloride and the like, among which boron trifluorideis particularly preferable. Examples of the organometallic compounds arediethylaluminum chloride, ethylaluminum chloride, diethylzinc and thelike.

An initiating terminal of the polymer, from which the polymerization ofthe polymer is initiated, is a hydrogen atom when water, alcohols orphenols is used. On the other hand, when acetals is used, the initiatingterminal is a hydrogen atom or a residue formed by eliminating one ofalkoxy groups from the used acetals. In addition, when the adduct ofvinyl ethers and carboxylic acid is used, the initiating terminal is aresidue formed by eliminating an alkylcarbonyloxy group originated inthe carboxylic acid from the adduct of vinyl ethers and carboxylic acid.

On the other hand, an end terminal, at which the polymerization of thepolymer is ended, is acetal, olefin or aldehyde when water, alcohols,phenols or acetals is used. When the adduct of vinyl ether andcarboxylic acid is used, the end terminal is carboxylic ester ofhemiacetal. The terminals of the polymer as described above may besubstituted by desirable group(s) by a known method. Examples of thedesirable group(s) are a saturated hydrocarbon residue, an etherresidue, an alcohol residue, a ketone residue, a nitril residue and anamid residue, among which a saturated hydrocarbon residue, an etherresidue and an alcohol residue are preferable.

Although depending on materials and initiators to be used, reaction ofthe polymerization can be initiated within a temperature range of −80 to150 degrees C., typically within a temperature range of −80 to 50degrees C. The reaction of the polymerization is ended in ten seconds toten hours after the initiation of the reaction. The reaction of thepolymerization is usually conducted under the presence of solvent. Thesolvent is not particularly limited as long as a sufficient amount ofthe reaction material can be dissolved in the solvent and the solvent isinactive against the reaction. Hydrocarbon-base solvent such as hexane,benzene or toluene and ether-base solvent such as ethyl ether,1,2-dimethoxyethane or tetrahydrofuran can be preferably used.

On the other hand, the polyvinyl ether copolymer III can be manufacturedby using alkylene glycol, polyalkylene glycol or monoether thereof asthe initiator and polymerizing the vinyl ether monomer in accordancewith the above polymerizing method.

Examples of the alkylene glycol, the polyalkylene glycol or themonoether thereof are alkylene glycol or polyalkylene glycol such asethylene glycol, diethylene glycol, triethylene glycol, polyethyleneglycol, propylene glycol, dipropylene glycol, tripropylene glycol orpolypropylene glycol, and alkylene glycol monoether or polyalkyleneglycol monoether such as ethylene glycol monomethylether, diethyleneglycol monomethylether, triethylene glycol monomethylether, propyleneglycol monomethylether, dipropylene glycol monomethylether, ortripropylene glycol monomethylether.

The vinyl ether monomers listed in the description of the polyvinylether I may be used as the materials for the polyvinyl ether copolymerIII. One of the above vinyl ether monomers may be singularly used or acombination of two or more thereof may be used.

In the invention, one of the above polyvinyl ether may be singularlyused or a combination of two or more thereof may be used.

When the polyvinyl ether-base compound(s) is used as the base oil of therefrigerator oil composition according to the invention, its kinematicviscosity at 40 degrees C. is preferably 1 to 400 mm²/s, more preferably5 to 250 mm²/s.

6 Polyalkylene Glycol (PAG)

An example of the polyalkylene glycol used in the base oil of therefrigerator oil composition according to the invention is a compoundrepresented by the following formula (3).

R⁹—[(OR¹⁰)_(m1)—OR¹¹]_(n1)  (3)

In the formula, R⁹ represents a hydrogen atom, an alkyl group having 1to 10 carbon atoms, an acyl group having 2 to 10 carbon atoms or analiphatic hydrocarbon group having 2 to 6 bonding sites and 1 to 10carbon atoms, R¹⁰ represents an alkylene group having 2 to 4 carbonatoms, R¹¹ represents a hydrogen atom, an alkyl group having 1 to 10carbon atoms or an acyl group having 2 to 10 carbon atoms, n1 representsan integer in a range of 1 to 6, and m1 represents a number that isdetermined such that the average value of ml multiplied by n1 is in arange of 6 to 80.

In the formula (3), the alkyl groups represented by R⁹ and R¹¹ each maybe linear, branched or cyclic. Examples of the alkyl groups are a methylgroup, an ethyl group, an n-propyl group, an isopropyl group, butylgroups, pentyl groups, hexyl groups, heptyl groups, octyl groups, nonylgroups, decyl groups, a cyclopentyl group, a cyclohexyl group and thelike. When the number of the carbon atoms contained in the alkylgroup(s) exceeds 10, compatibility of the base oil with the refrigerantis deteriorated, so that a phase separation may occur. The alkylgroup(s) preferably has 1 to 6 carbon atoms.

In addition, alkyl groups of the acyl groups represented by R⁹ and R¹¹each may be linear, branched or cyclic. Examples of the alkyl groups ofthe acyl groups are the same groups as listed in the above descriptionof the alkyl groups. The examples of the alkyl groups of the acyl groupseach have 1 to 9 carbon atoms. When the number of the carbon atomscontained in the acyl group(s) exceeds 10, compatibility of the base oilwith the refrigerant is deteriorated, so that a phase separation mayoccur. The acyl group(s) preferably has 2 to 6 carbon atoms.

When R⁹ and R¹¹ each represent an alkyl group or an acyl group, R⁹ andR¹¹ may be mutually the same or different.

In addition, when n1 is 2 or more, plural R⁹ included in one moleculemay be the same or mutually different.

When R⁹ is an aliphatic hydrocarbon group having 2 to 6 bonding sitesand 1 to 10 carbon atoms, the aliphatic hydrocarbon group may be linearor cyclic. Examples of the aliphatic hydrocarbon group having 2 bondingsites are an ethylene group, a propylene group, a butylene group, apentylene group, a hexylene group, a heptylene group, an octylene group,a nonylene group, a decylene group, a cyclopentylene group, acyclohexylene group and the like. An example of an aliphatic hydrocarbongroup having 3 to 6 bonding sites is a residue formed by eliminating ahydroxyl group from multivalent alcohol such as trimethylolpropane,glycerin, pentaerythritol, sorbitol, 1,2,3-trihydroxycyclohexane, or1,3,5-trihydroxycyclohexane.

When the number of the carbon atoms contained in the aliphatichydrocarbon group exceeds 10, compatibility of the base oil with therefrigerant is deteriorated, so that a phase separation may occur. Thealiphatic hydrocarbon group preferably has 2 to 6 carbon atoms.

In the formula (3), R¹⁰ represents an alkylene group having 2 to 4carbon atoms. Examples of an oxyalkylene group, which is a repeatingunit of the alkylene group, are an oxyethylene group, an oxypropylenegroup and an oxybutylene group. Although a plurality of oxyalkylenegroups included in one molecule may be mutually the same or different,at least one oxypropylene group is preferably included in one molecule.More preferably, an oxypropylene unit is contained in an oxyalkyleneunit with a content of 50 mol % or more.

In the formula (3), n1, which represents an integer in a range of 1 to6, is determined in accordance with the number of the bonding sites ofR⁹. For instance, n1 is 1 when R⁹ is an alkyl group or an acyl groupwhile n1 is 2, 3, 4, 5 or 6 when R⁹ is an aliphatic hydrocarbon grouphaving 2, 3, 4, 5 or 6 bonding sites respectively. In addition, m1 isdetermined so that the average value of m1 multiplied by n1 is in arange of 6 to 80. When the average value of m1 multiplied by n1 is notin the above range, an object of the invention will not be sufficientlyachieved.

The polyalkylene glycol represented by the formula (3) containspolyalkylene glycol having hydroxyl groups at its terminals. As long asthe content of the hydroxyl groups is 50 mol % or less of the totalterminal groups, the polyalkylene glycol containing the hydroxyl groupscan be preferably used. When the content of the hydroxyl groups is morethan 50 mol %, hygroscopicity is unfavorably increased, such thatviscosity index is decreased.

Polyalkylene glycols such as polypropylene glycol dimethylether,polyoxyethylene, polypropylene glycol dimethylether, polypropyleneglycol monobutylether or polypropylene glycol diacetate are preferablein view of cost and effects. Incidentally, in a copolymer that includesa polyoxypropylene (PO) unit and a polyoxyethylene (EU) unit such aspolyoxypropylene polyoxyethylene copolymer dimethyl ether, a molar ratioof PO/EO may belong to a range from 99:1 to 10:90, and the copolymer maybe a random copolymer or a block copolymer.

The polyalkylene glycol represented by the formula (3) may be any one ofthe compounds described in detail in JP-A-02-305893.

In the invention, one of the polyalkylene glycol may be singularly usedor a combination of two or more thereof may be used.

When the compound(s) is used as the base oil of the refrigerator oilcomposition according to the invention, its kinematic viscosity at 40degrees C. is preferably 1 to 400 mm²/s, more preferably 5 to 250 mm²/s.

(7) Polycarbonate-Base Compound

A polycarbonate-base compound used in the base oil of the refrigeratoroil composition according to the invention is preferably polycarbonatehaving two or more carbonate bonds in one molecule, i.e., at least onecompound selected from a group consisting of a compound represented bythe following formula (4) and a compound represented by the followingformula (5).

In the formula: Z represents a residue formed by eliminating a hydroxylgroup from c-valent alcohol having 1 to 12 carbon atoms; R¹² representsa linear or branched alkylene group having 2 to 10 carbon atoms; R¹³represents a monovalent hydrocarbon group having 1 to 12 carbon atoms ora group containing an ether bond represented by R¹⁵(O—R¹⁴)d-, where R¹⁵represents a hydrogen atom or a monovalent hydrocarbon group having 1 to12 carbon atoms, R¹⁴ represents a linear or branched alkylene grouphaving 2 to 10 carbon atoms, and d represents an integer in a range of 1to 20; a represents an integer in a range of 1 to 30; b represents aninteger in a range of 1 to 50; and c represents an integer in a range of1 to 6.

In the formula, R¹⁶ represents a linear or branched alkylene grouphaving 2 to 10 carbon atoms; e represents an integer in a range of 1 to20; and Z, R¹², R¹³, a, b and c each represent the same as in the above.

In the formulae (4) and (5), Z represents a residue formed byeliminating a hydroxyl group from 1 to 6-valent alcohol having 1 to 12carbon atoms. More preferably, Z represents a residue formed byeliminating a hydroxyl group from monovalent alcohol having 1 to 12carbon atoms.

Examples of 1 to 6-valent alcohol having 1 to 12 carbon atoms, whoseresidue corresponds to Z, are: monovalent alcohol such as aliphaticmonovalent alcohol exemplified by methyl alcohol, ethyl alcohol, n- orisopropyl alcohol, butyl alcohols, pentyl alcohols, hexyl alcohols,octyl alcohols, decyl alcohols and dodecyl alcohols, alicyclicmonovalent alcohol exemplified by cyclopentyl alcohol and cyclohexylalcohol, aromatic alcohol exemplified by phenol, cresol, xylenol,butylphenol and naphthol, or aromatic aliphatic alcohol exemplified bybenzyl alcohol and phenethyl alcohol; divalent alcohol such as aliphaticalcohol exemplified by ethylene glycol, propylene glycol, butyleneglycol, neo-pentylene glycol and tetramethylene glycol, alicyclicalcohol exemplified by cyclohexanediol and cyclohexanedimethanol, oraromatic alcohol exemplified by catechol, resorcinol, hydroquinone anddihydroxydiphenyl; trivalent alcohol such as aliphatic alcoholexemplified by glycerin, trimethylolpropane, trimethylolethane,trimethylolbutane and 1,3,5-pentanetriol, alicyclic alcohol exemplifiedby cyclohexanetriol and cyclohexanetrimethanol, or aromatic alcoholexemplified by pyrogallol and methylpyrogallol; and 4 to 6-valentalcohol such as aliphatic alcohol exemplified by pentaerythritol,diglycerin, triglycerin, sorbitol and dipentaerythritol.

An example of the polycarbonate compound represented by the formula (4)is a compound represented by the formula (4-a), and/or an example of thepolycarbonate compound represented by the formula (5) is a compoundrepresented by the formula (5-a).

In the formula, R¹⁷ represents a residue formed by eliminating ahydroxyl group from monovalent alcohol having 1 to 12 carbon atoms, andR¹², R¹³, a and b each represent the same as above.

In the formula, R¹², R¹³, R¹⁶, R¹⁷, a, b and e each represent the sameas above.

In the formulae (4-a) and (5-a), examples of the residue represented byR¹⁷ (the residue formed by eliminating a hydroxyl group from monovalentalcohol having 1 to 12 carbon atoms) are an aliphatic hydrocarbon groupsuch as a methyl group, an ethyl group, an n-propyl group, an isopropylgroup, butyl groups, pentyl groups, hexyl groups, octyl groups, decylgroups or dodecyl groups, an alicyclic hydrocarbon group such as acyclopentyl group, a cyclohexyl group, a methylcyclohexyl group, adimethylcyclohexyl group or a decahydronaphthyl group, an aromatichydrocarbon group such as a phenyl group, tolyl groups, xylyl groups, amesityl group or naphthyl groups, and aromatic aliphatic hydrocarbongroup such as a benzyl group, a methyl benzyl group, a phenethyl groupor naphthylmethyl groups. Among the above, a linear or branched alkylgroup having 1 to 6 carbon atoms is preferable.

R¹² represents a linear or branched alkylene group having 2 to 10 carbonatoms. The alkylene group preferably has 2 to 6 carbon atoms. Inaddition, an ethylene group and a propylene group are particularlypreferable in view of performance and manufacturing simplicity. R¹³represents a monovalent hydrocarbon group having 1 to 12 carbon atoms ora group containing an ether bond represented by R¹⁵(O—R¹⁴)d-, where R¹⁵represents a hydrogen atom or a monovalent hydrocarbon group having 1 to12 carbon atoms (preferably 1 to 6 carbon atoms), R¹⁴ represents alinear or branched alkylene group having 2 to 10 carbon atoms, and drepresents an integer in a range of 1 to 20. Examples of the monovalenthydrocarbon group having 1 to 12 carbon atoms are the same as thoselisted in the description of R¹⁷. The linear or branched alkylene grouphaving 2 to 10 carbon atoms represented by R¹⁴ preferably has 2 to 6carbon atoms for the same reason as described in relation to R¹². Inaddition, an ethylene group and a propylene group are particularlypreferable.

R¹³ preferably represents a linear or branched alkyl group having 1 to 6carbon atoms.

Although a variety of methods of manufacturing is available for theabove polycarbonate-base compound, a target polycarbonate-base compoundcan be typically manufactured by reacting a carbonate ester-formingderivative (e.g., carbonate diester, phosgene or the like) with alkyleneglycol or polyoxyalkylene glycol in accordance with a known method.

In the invention, one of the polycarbonate-base compounds may besingularly used or a combination of two or more thereof may be used.

When the polycarbonate-base compound(s) is used as the base oil of therefrigerator oil composition according to the invention, its kinematicviscosity at 40 degrees C. is preferably 1 to 400 mm²/s, more preferably5 to 250 mm²/s.

(8) Polyol Ester-Base Compound

An example of an polyol ester-base compound used in the base oil of therefrigerator oil composition according to the invention is ester ofpolyol having approximately 3 to 20 diols or hydroxyl groups andaliphatic acid having approximately 1 to 24 carbon atoms. Examples ofthe diol are ethylene glycol, 1,3-propanediol, propylene glycol,1,4-butanediol, 1,2-butanediol, 2-methyl-1,3-propanediol,1,5-pentanediol, neopentyl glycol, 1,6-hexanediol,2-ethyl-2-methyl-1,3-propanediol, 1,7-heptanediol,2-methyl-2-propyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol,1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol,1,12-dodecanediol and the like. Examples of the polyol are multivalentalcohol such as trimethylolethane, trimethylolpropane,trimethylolbutane, di-(trimethylolpropane), tri-(tromethylolpropane),pentaerythritol, di-(pentaerythritol), tri-(pentaerythritol), glycerin,polyglycesin (2 to 20-meric glycerin), 1,3,5-pentanetriol, sorbitol,sorbitan, sorbitol-glycerin condensation, adonitol, arabitol, xylitol ormannitol, sugars such as xylose, arabinose, ribose, rhamnose, glucose,fructose, galactose, mannose, sorbose, cellobiose, maltose, isomaltose,trehalose, sucrose, raffinose, gentianose or melezitose,partially-etherified compounds of the above, methyl glucoside(glycoside) and the like. Among the above, the polyol is preferablyhindered alcohol such as neopentyl glycol, trimethylol ethane,trimethylol propane, trimethylol butane, di-(trimethylol propane),tri-(trimethylol propane), pentaerythritol, di-(pentaerythritol) ortri-(pentaerythritol).

Although the number of the carbon atoms contained in the aliphaticacid(s) is not subject to any specific limitations, aliphatic acid(s)having 1 to 24 carbon atoms is typically used. Among the aliphatic acidshaving 1 to 24 carbon atoms, an aliphatic acid having 3 or more carbonatoms is preferable in view of lubricity, an aliphatic acid having 4 ormore carbon atoms is more preferable, an aliphatic acid having 5 or morecarbon atoms is further more preferable, and an aliphatic acid having 10or more carbon atoms is the most preferable. In addition, in view ofcompatibility of the base oil with the refrigerant, an aliphatic acidhaving 18 or less carbon atoms is preferable, an aliphatic acid having12 or less carbon atoms is more preferable, and an aliphatic acid having9 or less carbon atoms is further more preferable.

The aliphatic acid may be linear or branched. The aliphatic acid ispreferably linear in view of lubricity while the aliphatic acid ispreferably branched in view of hydrolytic stability. Further, thealiphatic acid may be saturated or unsaturated.

Examples of the aliphatic acid are linear or branched acids such as apentane acid, a hexane acid, a heptane acid, an octane acid, a nonaneacid, a decane acid, an undecane acid, a dodecane acid, a tridecaneacid, a tetradecane acid, a pentadecane acid, a hexadecane acid, aheptadecane acid, an octadecane acid, nonadecane acid, an icosane acidand an oleic acid, and a so-called neo-acid having quaternary a carbonatom. Specific examples of the above are a valeric acid (n-pentaneacid), a caproic acid (n-hexane acid), an enanthic acid (n-heptaneacid), a caprylic acid (n-octane acid), a pelargonic acid (n-nonaneacid), a capric acid (n-decane acid), an oleic acid (cis-9-octadeceneacid), an isopentane acid (3-methylbutane acid), a 2-methylhexane acid,a 2-ethylpentane acid, a 2-ethylhexane acid, a 3,5,5-trimethylhexaneacid and the like.

The polyol ester may be a partial ester in which some hydroxyl groups ofpolyol remain unesterified, a full ester in which all the hydroxylgroups are esterified or a mixture of a partial ester and a full ester.The polyol ester is preferably a full ester.

Among the above polyol esters, ester of hindered alcohol such asneopentyl glycol, trimethylol ethane, trimethylol propane, trimethylolbutane, di-(trimethylol propane), tri-(trimethylol propane),pentaerythritol, di-(pentaerythritol) and tri-(pentaerythritol) ispreferable in view of hydrolytic stability. The polyol ester is morepreferably ester of neopentyl glycol, trimethylol ethane, trimethylolpropane, trimethylol butane or pentaerythritol. The polyol ester is themost preferably ester of pentaerythritol because ester ofpentaerythritol is particularly excellent in the compatibility with therefrigerant and hydrolytic stability.

Preferable examples of the polyol ester-base compound are diester ofneopentyl glycol and one or more aliphatic acid(s) selected from a groupconsisting of a valeric acid, a caproic acid, an enanthic acid, acaprylic acid, a pelargonic acid, a capric acid, an oleic acid, anisopentane acid, a 2-methylhexane acid, a 2-ethylpentane acid, a2-ethylhexane acid and a 3,5,5-trimethylhexane acid, triester oftrimethylol ethane and one or more aliphatic acid(s) selected from agroup consisting of a valeric acid, a caproic acid, an enanthic acid, acaprylic acid, a pelargonic acid, a capric acid, an oleic acid, anisopentane acid, a 2-methylhexane acid, a 2-ethylpentane acid, a2-ethylhexane acid and a 3,5,5-trimethylhexane acid, triester oftrimethylol propane and one or more aliphatic acid(s) selected from agroup consisting of a valeric acid, a caproic acid, an enanthic acid, acaprylic acid, a pelargonic acid, a capric acid, an oleic acid, anisopentane acid, a 2-methylhexane acid, a 2-ethylpentane acid, a2-ethylhexane acid and a 3,5,5-trimethylhexane acid, triester oftrymethylol butane and one or more aliphatic acid(s) selected from agroup consisting of a valeric acid, a caproic acid, an enanthic acid, acaprylic acid, a pelargonic acid, a capric acid, an oleic acid, anisopentane acid, a 2-methylhexane acid, a 2-ethylpentane acid, a2-ethylhexane acid and a 3,5,5-trimethylhexane acid, and tetraester ofpentaerythritol and one or more aliphatic acid(s) selected from a groupconsisting of a valeric acid, a caproic acid, an enanthic acid, acaprylic acid, a pelargonic acid, a capric acid, an oleic acid, anisopentane acid, a 2-methylhexane acid, a 2-ethylpentane acid, a2-ethylhexane acid and a 3,5,5-trimethylhexane acid.

In the invention, one of the polyol ester-base compounds may besingularly used or a combination of two or more thereof may be used.

When the polyol ester-base compound(s) is used as the base oil of therefrigerator oil composition according to the invention, its kinematicviscosity at 40 degrees C. is preferably 1 to 400 mm²/s, more preferably5 to 250 mm²/s.

(9) Ether-Base Compound

In the refrigerator oil composition according to the invention, anether-based compound having a structure represented by the followingformula (1) is preferably used in the base oil.

Ra-[(ORb)n—(B)—(ORc)k]x-Rd  (1)

In the formula (1): Ra and Rd each represent a hydrogen atom, an alkylgroup having 1 to 10 carbon atoms, an acyl group having 2 to 10 carbonatoms or a hydrocarbon group having 2 to 6 bonding sites and 1 to 10carbon atoms; Rb and Rc each represent an alkylene group having 2 to 4carbon atoms; n and k each represent an integer in a range of 0 to 20; xrepresents an integer in a range of 1 to 6. (B) represents apolymerization site containing 3 or more monomer units each representedby a formula (2) as follows,

In the formula (2), R⁴, R⁵ and R⁶ each represent a hydrogen atom or ahydrocarbon group having 1 to 8 carbon atoms. R⁴, R⁵ and R⁶ may bemutually the same or different.

The hydrocarbon group specifically means an alkyl group of a methylgroup, an ethyl group, an n-propyl group, an isopropyl group, an n-butylgroup, an isobutyl group, a sec-butyl group, a tert-butyl group, pentylgroups, hexyl groups, heptyl groups or octyl groups, a cycloalkyl groupof a cyclopentyl group, a cyclohexyl group, methylcyclohexyl groups,ethylcyclohexyl groups, dimethylcyclohexyl groups or the like, an arylgroup of a phenyl group, methylphenyl groups, ethylphenyl groups ordimethylphenyl groups, or an arylalkyl group of a benzyl group,phenylethyl groups or methylbenzyl groups. R⁴, R⁵ and R⁶ each preferablyrepresent a hydrogen atom in view of stability of synthesizing reaction.

On the other hand, R⁷ represents a divalent hydrocarbon group having 1to 10 carbon atoms or an ether-bonded oxygen-containing divalenthydrocarbon group having 2 to 20 carbon atoms. Examples of the divalenthydrocarbon group having 1 to 10 carbon atoms are: a divalent aliphaticgroup such as a methylene group, an ethylene group, a phenylethylenegroup, a 1,2-propylene group, a 2-phenyl-1,2-propylene group, a1,3-propylene group, butylene groups, pentylene groups, hexylene groups,heptylene groups, octylene groups, nonylene groups or decylene groups;an alicyclic group having two bonding sites at an alicyclic hydrocarbonsuch as cyclohexane, methylcyclohexane, ethylcyclohexane,dimethylcyclohexane or propylcyclohexan; a divalent aromatic hydrocarbongroup such as phenylene groups, methylphenylene groups, ethylphenylenegroups, dimethylphenylene groups or naphthylene groups; an alkylaromatic group having a monovalent bonding site respectively in an alkylgroup portion and an aromatic group portion of alkyl aromatichydrocarbon such as toluene, xylene, or ethylbenzene; and an alkylaromatic group having a bonding site in an alkyl group portion ofpolyalkyl aromatic hydrocarbon such as xylene or diethylbenzene. Amongthe above, the aliphatic group having 2 to 4 carbon atoms isparticularly preferable in view of the compatibility of the base oilwith the refrigerant.

Preferable examples of the ether-bonded oxygen-containing divalenthydrocarbon group having 2 to 20 carbon atoms are a methoxymethylenegroup, a methoxyethylene group, a methoxymethylethylene group, a1,1-bis-methoxymethylethylene group, a 1,2-bis-methoxymethylethylenegroup, an ethoxymethylethylene group, a (2-methoxyethoxy)methylethylenegroup, a (1-methyl-2-methoxy)methylethylene group and the like. In theformula (2), m represents the number of units R⁷O, an average value ofwhich is 0 to 10, preferably 0 to 5. When plural m are present, theplural m may be mutually the same or different per unit. When pluralunits of R⁷O are contained, the plural units of R⁷O may be mutually thesame or different. When both k and n are 0, m is an integer of 1 or morein the formula (2).

R⁸ represents a hydrogen atom or a hydrocarbon group having 1 to 20carbon atoms. The hydrocarbon group specifically means an alkyl group ofa methyl group, an ethyl group, an n-propyl group, an isopropyl group,an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butylgroup, pentyl groups, hexyl groups, heptyl groups, octyl groups, nonylgroups, decyl groups or the like, a cycloalkyl group of a cyclopentylgroup, a cyclohexyl group, methylcyclohexyl groups, ethylcyclohexylgroups, propylcyclohexyl groups, dimethylcyclohexyl groups or the like,an aryl group of a phenyl group, methylphenyl groups, ethylphenylgroups, dimethylphenyl groups, propylphenyl groups, trimethylphenylgroups, butylphenyl groups, naphthyl groups or the like, or an arylalkylgroup of a benzyl group, phenylethyl groups, methylbenzyl groups,phenylpropyl groups, phenylbutyl groups or the like. Plural R⁴ to R⁸ ofthe plural units may be mutually the same or different per unit.

By copolymerizing the ether-base compound having the monomer unitrepresented by the formula (2), lubricity, insulation properties,hygroscopicity and the like can be enhanced while a sufficient level ofthe compatibility with the refrigerant is retained. At this time, bysuitably selecting a type of the monomer used as the material, a type ofthe initiator and a copolymer ratio, the level of the above performanceof the refrigerator oil composition can be set at a target level.Accordingly, it is possible to obtain an oil composition that canexhibit required levels of lubricity and compatibility that varydepending on: types of compressors used in freezing or air-conditioningsystems to which lubricating oil is applied; materials and freezingcapabilities of lubricating portions; and types of refrigerants.

In the ether-base compound represented by the formula (1), (B)represents a polymerization site containing three or more monomer unitseach represented by the formula (2). The number of the monomer units(i.e., polymerization degree) can be suitably determined in accordancewith a desired level of kinematic viscosity. The polymerization degreeis typically determined so that the kinematic viscosity at 100 degreesC. becomes preferably 1 to 50 mm²/s, more preferably 2 to 50 mm²/s,further more preferably 5 to 50 mm²/s, particularly preferably 5 to 20mm²/s.

Preferably in the ether-base compound represented by the formula (1),its molar ratio of carbon to oxygen (molar ratio of carbon/oxygen) is 4or less. When the molar ratio is more than 4, the compatibility of thecompound with a natural refrigerant such as carbon dioxide isdeteriorated.

Instead of representing a homopolymer site containing the monomer unitseach represented by the formula (2), (B) in the formula (1) mayrepresent a block copolymer site or a random copolymer site containingthe monomer unit(s) represented by the formula (2) and monomer unit(s)represented by the following formula (6).

In the formula (6), R¹⁸ to R²¹ each represent a hydrogen atom or ahydrocarbon group having 1 to 20 carbon atoms. R¹⁸ to R²¹ may bemutually the same or different. Examples of the hydrocarbon group having1 to 20 carbon atoms are the same as those of R⁸ in the formula (2). Inaddition, R¹⁸ to R²¹ of plural monomer units may be mutually the same ordifferent per monomer unit.

Polymerization degree of the ether-base compound represented by theformula (1), which contains a block or random copolymer containing themonomer unit represented by the formula (2) and the monomer unitrepresented by the formula (6), may be suitably determined in accordancewith a desired level of kinematic viscosity. The polymerization degreeis typically determined such that the kinematic viscosity at 100 degreesC. preferably becomes 5 mm²/s or more, more preferably 5 to 20 mm²/s.Preferably in the ether-base compound, its molar ratio of carbon/oxygenis 4 or less. When the molar ratio is more than 4, the compatibility ofthe compound with a natural refrigerant such as carbon dioxide isdeteriorated.

The above ether-base compound can be manufactured by polymerizing therelevant vinyl ether-base monomer or by copolymerizing the relevanthydrocarbon monomer having olefin double-bond(s) and the relevant vinylether-base monomer.

In view of stability of synthesizing reaction, the ether-base compoundis preferably structured such that, in the formula (1), Ra represents ahydrogen atom and n equals to 0 at the first terminal of the compoundwhile Rd represents a hydrogen atom and k equals to 0 at the secondterminal of the compound.

Such an ether-base compound can be manufactured by performing suchpolymerization on a monomer as radical polymerization, cationpolymerization or radiation polymerization. For instance, bypolymerizing a vinyl ether-base monomer in accordance with the followingmethod, the obtained polymer of the vinyl ether-base monomer can exhibita desired level of viscosity. At the initial stage of thepolymerization, a compound prepared by combining Bronsted acids, Lewisacids or organometallic compounds with water, alcohols, phenols, acetalsor an adduct of vinyl ethers and a carboxylic acid may be used. Examplesof the Bronsted acids are hydrofluoric acid, hydrochloric acid,hydrobromic acid, hydroiodic acid, nitric acid, sulfuric acid,trichloroacetic acid, trifluoroacetic acid and the like. Examples of theLewis acids are boron trifluoride, aluminum trichloride, aluminumtribromide, tin tetrachloride, zinc dichloride, ferric chloride and thelike, among which boron trifluoride is particularly preferable. Examplesof the organometallic compounds are diethylaluminum chloride,ethylaluminum chloride, diethylzinc and the like.

Water, alcohols, phenols, acetals or an adduct of vinyl ethers and acarboxylic acid that is to be combined with the above may be suitablydetermined. Examples of the alcohols are saturated aliphatic alcoholhaving 1 to 20 carbon atoms such as methanol, ethanol, propanol,isopropanol, butanol, isobutanol, sec-butanol, tert-butanol, pentanols,hexanols, heptanols or octanols, unsaturated aliphatic alcohol having 3to 10 carbon atoms such as aryl alcohol, monoether of alkylene glycolsuch as ethylene glycol monomethyl ether, diethylene glycol monomethylether, triethylene glycol monomethyl ether, propylene glycol monomethylether, dipropylene glycol monomethyl ether or tripropylene glycolmonomethyl ether, and the like. Examples of the carboxylic acid used forpreparing the adduct of vinyl ethers and the carboxylic acid are aceticacid, propionic acid, n-butyric acid, iso-butyric acid, n-valeric acid,iso-valeric acid, 2-methyl butyric acid, pivalic acid, n-caproic acid,2,2-dimethyl butyric acid, 2-methyl valeric acid, 3-methyl valeric acid,4-methyl valeric acid, enanthic acid, 2-methyl caproic acid, caprylicacid, 2-ethyl caproic acid, 2-n-propyl valeric acid, n-nonane acid,3,5,5-trimethyl caproic acid, caprylic acid, undecane acid and the like.

According to the invention, the mineral oil or the synthetic oilemployed as the base oil may be singularly used or a mixture thereof maybe used. In either case, the kinematic viscosity at 100 degrees C. maybe determined preferably at 1 to 50 mm²/s, more preferably at 3 to 50mm²/s, further more preferably at 5 to 30 mm², particularly preferablyat 5 to 20 mm²/s.

A molecular weight of the base oil is preferably in a range of 150 to5,000 in view of evaporation prevention, the flash point, performance asthe refrigerator oil and the like, more preferably in a range of 300 to3,000. A viscosity index of 60 or more is preferable.

A lubricating oil composition for refrigerator according to theinvention is formed by adding to a base oil an organic compound whosemolecules include double bond. It is preferable that this double bonddoes not accompany an aromatic ring structure in the invention.

Here, the organic compound containing a double bond in its moleculefunctions as an oxygen scavenger. In other words, the organic compoundremoves oxygen that is present in the refrigerator system in a verysmall amount by making the oxygen react with the double bond of theorganic compound.

Preferable examples of such an oxygen scavenger include an unsaturatedaliphatic compound and a terpene containing a double bond.

An employable unsaturated aliphatic compound includes unsaturatedhydrocarbon. Examples of the unsaturated hydrocarbon include olefin andpolyene such as diene or triene. The olefin preferably is α-olefin,which is more reactive with oxygen than internal olefin is. The α-olefinmay be, for example, 1-tetradecene, 1-hexadecene, or 1-octadecene.

In view of reactivity with oxygen, it is preferable that the unsaturatedaliphatic compound is, for example, an unsaturated aliphatic alcoholcontaining conjugated double bond such as vitamin A ((2E, 4E, 6E,8E)-3,7-dimethyl-9-(2,6,6-trimethylcyclohexe-1-yl)nona-2,4,6,8-tetraene-1-ol) represented by a molecular formula C₂₀H₃₀O.

The terpene preferably is terpene hydrocarbon containing a double bond.In view of reactivity with oxygen, terpene hydrocarbon containing aconjugated double bond such as α-farnesene (C₁₅H₂₄:3,7,11-trimethyldodeca-1,3,6,10-tetraene) or α-farnesene (C₁₅H₂₄:7,11-dimethyl-3-methylidenedodeca-1,6,10-triene) is preferable, forexample.

The organic compound having double bond in its molecule is preferablycontained in the composition with a content of 0.1 to 10 mass % of thetotal amount of the composition, more preferably 0.5 to 8 mass %,further more preferably 3 to 6 mass %. Satisfactory oxygen-scavengingperformance cannot be obtained with an oxygen scavenger contained inless than 0.1 mass % of the organic compound even if the oxygenscavenger has double bond in its molecule. In cases the contained oxygenscavenger is increased to more than 10 mass %, the compatibility withthe refrigerant is deteriorated, which may cause a two-layer separation.

Incidentally, although an aromatic ring such as a benzene ring alsoincludes double bond, a compound having an aromatic ring is not suitablefor an oxygen scavenger since such a compound is insufficiently reactivewith oxygen due to stability of the compound. However, a compoundincluding an aliphatic double bond as well as an aromatic ring can beutilized. For example, a styrene derivative or the like can be utilizedas an oxygen scavenger of the invention. Here, the aliphatic double bondmay or may not be in conjugated relationship with the aromatic ring.

Refrigerants to which the refrigerator oil composition according to theinvention is applied include saturated fluorohydrocarbon (HFC), carbondioxide (CO₂), low-boiling hydrocarbon (HC), and ammonia. Furthermore, arefrigerant containing at least one type of fluorine-containing organiccompound selected from compounds represented by the following molecularformula (A) or a combination of such a fluorine-containing compound anda saturated fluorohydrocarbon compound is preferred on account of thelow global warming potential.

C_(p)O_(q)F_(r)R_(s)  (A)

In the formula: R represents a Cl, Br, I or hydrogen atom, p is aninteger in a range of 1 to 6, q is an integer in a range of 0 to 2, r isan integer in a range of 1 to 14, and s is an integer in a range of 0 to13; and if q is 0, p is in a range of 2 to 6, and the molecule includesat least one carbon-carbon unsaturated bond.

The refrigerant represented by the above molecular formula (A) will bedescribed in detail below.

Molecular Formula

The molecular formula (A), which shows the types and numbers of theelements in the molecule, represents a fluorine-containing organiccompound in which the number p of carbon atoms C ranges from 1 to 6. Anyfluorine-containing organic compound having 1 to 6 carbon atomspossesses physical and chemical properties such as a boiling point, afreezing point and an evaporative latent heat required for arefrigerant.

In the molecular formula (A), the bond state of a quantity p of carbonatoms represented by C_(p) includes: unsaturated bond such ascarbon-carbon single bond and carbon-carbon double bond; andcarbon-oxygen double bond. The carbon-carbon unsaturated bond ispreferable in view of stability, and the number of the unsaturated bond,which is typically one or more, is preferably one.

In the formula (A), the bond state of a quantity q of oxygen atomsrepresented by O_(q) preferably is oxygen from an ether group, ahydroxyl group, or a carbonyl group. The number of oxygen atoms q may betwo, which includes cases in which two ether groups, hydroxyl groups orthe like are provided.

If q in O_(q) is zero, which means that the molecule does not includeoxygen atoms, p falls in a range of two to six, which means that themolecule includes one or more unsaturated bonds such as carbon-carbondouble bonds. In other words, at least one of the bonds of a quantity pof carbon atoms represented by C_(p) needs to be a carbon-carbonunsaturated bond.

Besides, in the formula (A), R represents Cl, Br, I, or H, any of whichmay be selected. However, R preferably is H on account of lesspossibility of destroying the ozone layer.

As set forth above, examples of the fluorine-containing organic compoundrepresented by the formula (A) include an unsaturated fluorohydrocarboncompound, a fluoroether compound, a fluoroalcohol compound, and afluoroketone compound.

These compounds will be described below.

Unsaturated Fluorohydrocarbon Compound

According to the invention, an example of an unsaturatedfluorohydrocarbon compound used as a freezer refrigerant is anunsaturated fluorohydrocarbon compound represented by the molecularformula (A) in which R is H, p is in a range of 2 to 6, q is 0, r is ina range of 1 to 12, and s is in a range of 0 to 11.

Preferred examples of such an unsaturated fluorohydrocarbon compoundinclude fluorinated compounds of a linear or branched chain olefinhaving 2 to 8 carbon atoms and a ring olefin having 4 to 6 carbon atoms.

The specific examples include ethylene to which 1 to 3 fluorine atomsare introduced, propene to which 1 to 5 fluorine atoms are introduced,butenes to which 1 to 7 fluorine atoms are introduced, pentenes to which1 to 9 fluorine atoms are introduced, hexenes to which 1 to 11 fluorineatoms are introduced, cyclobutene to which 1 to 5 fluorine atoms areintroduced, cyclopentene to which 1 to 7 fluorine atoms are introduced,and cyclohexene to which 1 to 9 fluorine atoms are introduced.

Among the above unsaturated fluorohydrocarbon compounds, an unsaturatedfluorohydrocarbon compound having 2 or 3 carbon atoms is preferred, andin particular, a fluorinated compound of propene is further preferred.Specifically, in view of the global warming potential, the compoundrepresented by the molecular formula (A) preferably is a compoundrepresented by one of the molecular formulae C₃HF₅, C₃H₂F₄, and C₃H₃F₃.Examples of the fluorinated compound of propene includes: a variety ofisomers of pentafluoropropene; 3,3,3-trifluoropropene; and2,3,3,3-tetrafluoropropene. Specifically, in view of low global warmingpotential, 1,2,3,3,3-pentafluoropropene (HFC1225ye) and2,3,3,3-tetrafluoropropene (HFC1234yf) are preferred.

In the invention, one of the unsaturated fluorohydrocarbon compounds maybe singularly used or a combination of two or more thereof may be used.

Besides, a combination of a saturated fluorohydrocarbon refrigeranthaving 1 or 2 carbon atoms and an unsaturated fluorohydrocarbonrefrigerant having 3 carbon atoms is also suitable. Examples of such acombination includes a combination of the above mentioned HFC1225ye andCH₂F₂ (HFC32), a combination of HFC1225ye and CHF₂CH₃ (HFC152a), and acombination of the above mentioned HFC1234yf and CF₃I.

Fluoroether Compound

According to the invention, an example of a fluoroether compound used asa freezer refrigerant is an unsaturated fluoroether compound representedby the molecular formula (A) in which R is H, p is in a range of 2 to 6,q is 1 or 2, r is in a range of 1 to 14, and s is in a range of 0 to 13.

Preferable examples of such a fluoroether compound include: afluorinated compound of chain aliphatic ether having 2 to 6 carbon atomsand 1 or 2 ether bonds in which the alkyl base is linear or branched;and a fluorinated compound of ring aliphatic ether having 3 to 6 carbonatoms and 1 or 2 ether bond.

The specific examples include dimethyl ether to which 1 to 6 fluorineatoms are introduced, methylether to which 1 to 8 fluorine atoms areintroduced, dimethoxymethane to which 1 to 8 fluorine atoms areintroduced, methylpropylethers to which 1 to 10 fluorine atoms areintroduced, methylbutylethers to which 1 to 12 fluorine atoms areintroduced, ethylpropylethers to which 1 to 12 fluorine atoms areintroduced, oxetanes to which 1 to 6 fluorine atoms are introduced,1,3-dioxolan to which 1 to 6 fluorine atoms, tetrahydrofuran to which 1to 8 fluorine atoms are introduced.

Examples of the fluorinated ether compound include hexafluoro dimethylether, pentafluoro dimethyl ether, bis(difluoromethyl)ether,fluoromethyl trifluoromethyl ether, trifluoromethyl methyl ether,perfluorodimethoxymethane, 1-trifluoromethoxy-1,1,2,2-tetrafluoroethane,difluoromethoxy pentafluoroethane,1-trifluoromethoxy-1,2,2,2-tetrafluoroethane,1-difluoromethoxy-1,1,2,2-tetrafluoroethane,1-difluoromethoxy-1,2,2,2-tetrafluoroethane,1-trifluoromethoxy-2,2,2-trifluoroethane,1-difluoromethoxy-2,2,2-trifluoroethane, perfluorooxetane,perfluoro-1,3-dioxolan, a variety of isomers of pentafluorooxetane, anda variety of isomers of tetrafluorooxetane.

In the invention, one of the fluorinated ether compounds may besingularly used or a combination of two or more thereof may be used.

Fluorinated Alcohol Compound

According to the invention, an example of a fluorinated alcohol compoundrepresented by the general formula (A) used as a freezer refrigerant isa fluorinated ether compound represented by the molecular formula (A) inwhich R is H, p is in a range of 1 to 6, q is 1 or 2, r is in a range of1 to 13, and s is in a range of 1 to 13.

A preferable example of such a fluorinated alcohol compound is afluorinated compound of linear or branched aliphatic alcohol having 1 to6 carbon atoms and 1 or 2 hydroxyl groups.

The specific examples include methyl alcohol to which 1 to 3 fluorineatoms are introduced, ethyl alcohol to which 1 to 5 fluorine atoms areintroduced, propyl alcohols to which 1 to 7 fluorine atoms areintroduced, butyl alcohols to which 1 to 9 fluorine atoms areintroduced, pentyl alcohols to which 1 to 11 fluorine atoms areintroduced, ethylene glycol to which 1 to 4 fluorine atoms areintroduced, and propylene glycol to which 1 to 6 fluorine atoms areintroduced.

The specific examples of such a fluorinated alcohol compound include:monofluoromethyl alcohol, difluoromethyl alcohol, trifluoromethylalcohol, isomers of difluoroethyl alcohol, isomers oftrifluoroethylalcohol, isomers of tetrafluoroethyl alcohol,pentafluoroethylalcohol, isomers of difluoropropyl alcohol, isomers oftrifluoropropyl alcohol, isomers of tetrafluoropropyl alcohol, isomersof pentafluoropropyl alcohol, isomers of hexafluoropropyl alcohol,heptafluoropropyl alcohol, isomers of difluorobutyl alcohol, isomers oftrifluorobutyl alcohol, isomers of tetrafluorobutyl alcohol, isomers ofpentafluorobutyl alcohol, isomers of hexafluorobutyl alcohol, isomers ofheptafluorobutyl alcohol, isomers of octafluorobutyl alcohol,nonafluorobutyl alcohol, isomers of difluoroethylene glycol,trifluoroethylene glycol, and tetrafluoroethylene glycol. The specificexamples of the fluorinated alcohol compound further include: isomers ofdifluoropropylene glycol, isomers of trifluoropropylene glycol, isomersof tetrafluoropropylene glycol, isomers of pentafluoropropylene glycol,fluorinated propylene glycol such as hexafluoropropylene glycol, andfluorinated trimethylene glycol that corresponds to the fluorinatedpropylene glycol.

In the invention, one of the fluorinated alcohol compounds may besingularly used or a combination of two or more thereof may be used.

Fluorinated Ketone Compound

An example of a fluorintate ketone compound used as a freezerrefrigerant according to the invention includes a fluorinated ketonecompound represented by the molecular formula (A) in which R is H, p isin a range of 2 to 6, q is 1 or 2, r is in a range of 1 to 12, and s isin a range of 0 to 11.

A preferable example of such a fluorinated ketone compound is afluorinated compound of aliphatic ketone having 3 to 6 carbon atoms inwhich the alkyl group is linear or branched.

The specific examples include acetone to which 1 to 6 fluorine atoms areintroduced, methylethyl ketone to which 1 to 8 fluorine atoms areintroduced, diethylketone to which 1 to 10 fluorine atoms areintroduced, and methylpropyl ketones to which 1 to 10 fluorine atoms areintroduced.

Examples of the fluorinated ketone compound include: hexafluoro dimethylketone, pentafluoro dimethyl ketone, bis(difluoromethyl)ketone,fluoromethyl trifluoromethyl ketone, trifluoromethyl methyl ketone,perfluoromethyl ethyl ketone, trifluoromethyl-1,1,2,2-tetrafluoroethylketone, difluoromethyl pentafluoroethyl ketone,trifluoromethyl-1,1,2,2-tetrafluoroethyl ketone,difluoromethyl-1,1,2,2-tetrafluoroethyl ketone,difluoromethyl-1,2,2,2-tetrafluoroethyl ketone,trifluoromethyl-2,2,2-trifluoroethyl ketone, anddifluoromethyl-2,2,2-trifluoroethyl ketone.

In the invention, one of the fluorinated ketone compounds may besingularly used or a combination of two or more thereof may be used.

Saturated Fluorohydrocarbon Compound

The saturated fluorohydrocarbon compound is a refrigerant that may bemixed, as necessary, with the fluorine-containing organic compounds, atleast one of which is selected from the compounds represented by theabove general formula (A).

A preferred saturated fluorohydrocarbon compound is a fluorinatedcompound of alkane having 1 to 4 carbon atoms. In particular,fluorinated compounds of methane and ethane having 1 or 2 carbon atomssuch as trifluoromethane, difluoromethane, 1,1-difluoroethane,1,1,1-trifluoroethane, 1,1,2-trifluoroethane, 1,1,1,2-tetrafluoroethane,1,1,2,2-tetrafluoroehtane, 1,1,1,2,2-pentafluoroethane are favorable.The saturated fluorohydrocarbon compound may be the above-mentionedfluorinated alkane that has undergone halogenation by a halogen atomother than fluorine in addition to fluorination. An example of such asaturated fluorohydrocarbon compound includes trifluoroiodomethane(CF₃I). One of the saturated fluorohydrocarbon compounds may besingularly used or a combination of two or more thereof may be used.

The saturated fluorohydrocarbon compound is typically contained in therefrigerant in 30 mass % or less of the total amount of the refrigerant,preferably in 20 mass % or less and further preferably in 10 mass % orless.

The refrigerator oil composition of the invention may be added with atleast one additive selected from a group consisting of an extremepressure agent, an oiliness agent, an antioxidant, an acid scavenger, ametal deactivator and an antifoaming agent as long as an object of theinvention can be achieved.

Examples of the extreme pressure agent are phosphorus-base extremepressure agents such as phosphate ester, acid phosphate ester, phosphiteester, acid phosphite ester and amine salts thereof.

Among the above phosphorus-base extreme pressure agents, tricresylphosphate, trithiophenyl phosphate, tri(nonylphenyl)phosphite, dioleylhydrogen phosphite, 2-ethylhexyl diphenyl phosphite and the like areparticularly preferable in view of extreme pressure properties, frictioncharacteristics and the like.

Another example of the extreme pressure agent is a metal salt ofcarboxylic acid. The metal salt of carboxylic acid is preferably a metalsalt of carboxylic acid having 3 to 60 carbon atoms, more preferably ametal salt of carboxylic acid having 3 to 30 carbon atoms, particularlypreferably a metal salt of aliphatic acid having 12 to 30 carbon atoms.The metal salt of carboxylic acid may be a metal salt of dimer acid ortrimer acid of the aliphatic acid, or a metal salt of dicarboxylic acidhaving 3 to 30 carbon atoms. Among the above, a metal salt of aliphaticacid having 12 to 30 carbon atoms and a metal salt of dicarboxylic acidhaving 3 to 30 carbon atoms are particularly preferable.

On the other hand, a metal of the metal salt is preferably an alkalimetal or an alkali earth metal. Particularly, an alkali metal issuitable.

Further examples of the extreme pressure agent other than theabove-listed examples are sulfur-base extreme pressure agents such assulfurized fat and oil, sulfurized aliphatic acid, ester sulfide, olefinsulfide, dihydrocarbyl polysulfide, thiocarbamates, thioterpenes,dialkylthiodipropionates and the like.

The extreme pressure agent is contained in the composition preferablywith a content of 0.001 to 10 mass % of the total amount of thecomposition, further preferably with a content of 0.01 to 5 mass % andparticularly preferably with a content of 0.05 to 3 mass %.

One of the above extreme pressure agents may be singularly used or acombination of two or more thereof may be used.

Examples of the oiliness agent are saturated or unsaturated aliphaticmonocarboxyl acid such as stearic acid or oleic acid, dimerizedaliphatic acid such as dimer acid or hydrogenated dimer acid, hydroxyaliphatic acid such as ricinoleic acid or 12-hydroxystearic acid,saturated or unsaturated aliphatic monoalcohol such as lauryl alcohol oroleyl alcohol, saturated or unsaturated aliphatic monoamine such asstearylamine or oleylamine, saturated or unsaturated monocarboxyl acidamide such as lauric acid amide or oleic acid amide, partial ester ofmultivalent alcohol such as glycerin or sorbitol and saturated orunsaturated monocarboxyl acid, and the like.

One of the above oiliness agents may be singularly used or a combinationof two or more thereof may be used. The oiliness agent is typicallycontained in the composition with a content of 0.01 to 10 mass % of thetotal amount of the composition, preferably with a content of 0.1 to 5mass %.

Examples of the antioxidant include phenol-base antioxidant such as2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol or2,2′-methylenebis(4-methyl-6-tert-butylphenol) and amine-baseantioxidant such as phenyl-α-naphthylamine orN,N′-diphenyl-p-phenylenediamine. In view of effects and cost, theantioxidant is typically contained in the composition with a content of0.01 to 5 mass %, preferably with a content of 0.05 to 3 mass %.

Examples of the acid scavenger include epoxy compounds such as phenylglycidyl ether, alkyl glycidyl ether, alkylene glycol glycidyl ether(e.g., polypropylene glycol glycidyl ether), cyclohexene oxide, α-olefinoxide and epoxidized soybean oil. Among the above, phenyl glycidylether, alkyl glycidyl ether, alkylene glycol glycidyl ether, cyclohexeneoxide and α-olefin oxide are preferable in view of compatibility.

An alkyl group of alkyl glycidyl ether and an alkylene group of alkyleneglycol glycidyl ether each may be branched, and each typically have 3 to30 carbon atoms, preferably 4 to 24 carbon atoms, particularlypreferably 6 to 16 carbon atoms. In addition, α-olefin oxide having 4 to50 carbon atoms in total is typically used, α-olefin oxide having 4 to24 carbon atoms in total is more preferably used, and α-olefin oxidehaving 6 to 16 carbon atoms in total is particularly preferably used. Inthe invention, one of the above acid scavengers may be singularly usedor a combination of two or more thereof may be used. In view of effectsand sludge prevention, the acid scavenger is typically contained in thecomposition with a content of 0.005 to 5 mass % of the total amount ofthe composition, particularly preferably with a content of 0.05 to 3mass %.

By adding such an acid scavenger to the composition, stability of therefrigerator oil composition according to the invention can be moreenhanced. By using the extreme pressure agent and the antioxidanttogether with the acid scavenger, the stability of the composition canbe further more enhanced.

An example of the metal deactivator is N—[N′,N′-dialkyl (alkyl grouphaving 3 to 12 carbon atoms) aminomethyl]tolutriazole or the like.Examples of the antifoaming agent are silicone oil, fluorinated siliconeoil and the like.

The refrigerator oil composition according to the invention preferablyhas viscosity at 40 degrees C. of 1 to 400 mm²/s, more preferably 3 to300 mm²/s, further more preferably 5 to 200 mm²/s. Volume resistivity ofthe composition is preferably 10⁹ Ω·cm or more, more preferably 10¹⁰Ω·cm or more, the upper limit of which is typically approximately 10¹¹Ω·cm. Friction coefficient of the composition obtained throughreciprocating friction test(s) is preferably 0.119 or less, morepreferably 0.117 or less, further more preferably 0.112 or less, thelower limit of which is typically approximately 0.07.

In the method of lubricating a freezer that uses the refrigerator oilcomposition according to the invention, used amounts of the refrigerantlisted above and the refrigerator oil composition are preferably in amass ratio (i.e., a mass ratio of the refrigerant/the refrigerator oilcomposition) of 99/1 to 10/90, more preferably in a mass ratio of 95/5to 30/70. When the used amount of the refrigerant is less than the abovemass ratio, the freezing capability of the refrigerant is unfavorablydeteriorated. On the other hand, when the used amount of the refrigerantis more than the above mass ratio, the lubricating capability of therefrigerator oil composition is unfavorably deteriorated.

Examples of a freezer (freezing system) to which the refrigerator oilcomposition according to the invention is preferably applied are: afreezing system that includes a compressor, a condenser, an expansionmechanism (capillary tube, expansion valve) and an evaporator asessential components; a freezing system including an ejector cycle; anda freezing system including a dryer (desiccant: natural or syntheticzeolite).

The above compressor may be open type, semi-hermetic type or hermetictype. A motor used in a hermetic-type compressor is an AC motor or a DCmotor. The compressor may be a rotary compressor, a scroll compressor, aswing compressor or a piston compressor. The compressor may be a smallcompressor of approximately 0.2 kW or a large compressor ofapproximately 30 kW.

In the freezing system, a water content within the system is preferably500 ppm by mass or less, more preferably 300 ppm by mass or less.Accordingly, a desiccant filled in the above-mentioned dryer ispreferably a desiccant formed of zeolite having a pore size of 0.33 nmor smaller. The zeolite, which may be natural zeolite or syntheticzeolite, preferably has a CO₂ gas absorption capacity of 1.0% or less at25 degrees C. and CO₂ gas partial pressure of 33 kPa. Examples of suchsynthetic zeolite include XH-9 (trade name) and XH-600 (trade name)manufactured by Union Showa K.K. With use of such desiccant, while wateris efficiently removed without absorption of refrigerant in therefrigerating cycle, the desiccant is prevented from powderization dueto deterioration. Accordingly, the choking of piping caused bypowderization, abnormal wear of a slide section of the compressor causedby invasion of the powderized desiccant into the slide section of thecompressor, and the like are prevented. Therefore, the freezer can bestably driven for a long time.

In addition, a partial pressure of residual air therein is preferably 13kPa or less, more preferably 10 kPa or less and still more preferably 5kPa or less.

The freezer to which the refrigerator oil composition according to theinvention is applied includes a variety of slide portions (e.g.,bearing) therein. In the invention, slide portions made of engineeringplastic or slide portions having organic coating layers or inorganiccoating layers are used in view of sealability.

The engineering plastic is preferably, for instance, a polyamide resin,a polyphenylene sulfide resin, a polyacetal resin or the like in view ofsealability, slidability, wear resistance and the like.

The organic coating layers each are preferably, for instance, a coatinglayer of a fluorine-containing resin (e.g., coating layer ofpolytetrafluoroethylene), a coating layer of polyimide, a coating layerof polyamide-imide or the like in view of sealability, slidability, wearresistance and the like.

On the other hand, the inorganic coating layers each are preferably, forinstance, a graphite layer, a diamond-like carbon layer, a nickel layer,a molybdenum layer, a tin layer, a chromium layer, a nitride layer, aboron layer or the like in view of sealability, slidability, wearresistance and the like. The inorganic coating layers each may be formedby plating, CVD (chemical vapor deposition) or PVD (physical vapordeposition).

The slide portions each may be made of conventional alloy such asFe-based alloy, Al-based alloy or Cu-based alloy.

The base oil of the refrigerator composition according to the inventionis an additive in the form of organic compounds (not including compoundsfrom the aromatic class) having a double bond in the molecule thereof.Accordingly, a small amount of oxygen remaining in the freezer systemcan be scavenged, thereby preventing oxygen from reacting with thechlorofluorocarbon refrigerant. Therefore, the freezer lubricating oilcomposition according to the invention can be stably used for a longtime in an application that employs an unsaturated chlorofluorocarbonrefrigerant reactive particularly with oxygen such as an automobile airconditioner, an automobile air conditioner with electric motor drivencompressor, a gas heat pump, an air conditioner, a refrigerator, avending machine, a showcase, hot-water supply systems, or a heating andrefrigerating system.

EXAMPLES

Now, the invention will be further described in detail by reference toExamples, which by no means limit the invention.

Examples 1 to 19 and Comparatives 1 to 10

Refrigerator oil compositions respectively structured as shown in Tables1 to 3 were made, and then a sealed tube test and an autoclave test asshown below were conducted to evaluate stability of the compositions.

Sealed Tube Test Examples 1 to 15 and Comparatives 1 to 9

A glass tube having an inner volume of 10 ml was sealed (no air) afterbeing filled with composition/refrigerant (in a ratio of 4 g/0.5 g; nowater) and a metal catalyst formed of iron, cupper, and aluminum. Then,after being preserved for 5 days at a temperature of 175° C., the glasstube was visually observed for the appearance of the composition, theappearance of the catalyst, and presence or absence of sludge.

Autoclave Test Examples 16 to 19 and Comparative 10

An autoclave having an inner volume of 200 ml was filled withcomposition/refrigerant (in a ratio of 30 g/10 g; 2000 mass ppm of waterin the composition) and a metal catalyst formed of iron, cupper, andaluminum and sealed (50 ml of air). Then, after being preserved for 90hours at a temperature of 175° C., the autoclave was visually observedfor the appearance of the composition, the appearance of the catalyst,and presence or absence of sludge, and the acid value was measured. Notethat the acid value was measured by potentiometry in accordance with“Determination of neutralization number for lubricants” as defined byJIS K2501.

Note that the following two types of refrigerants were used.

1 Examples 1 to 15 and Comparatives 1 to 9

A mixture refrigerant formed of 70 mass % of HFC1234yf(2,3,3,3-tetrafluoropropene) and 30 mass % of CF₃I(iodotrifluoromethane)

2 Examples 16 to 19 and Comparative 10

A mixture refrigerant formed of 96 mass % of HFC1225ye(1,2,3,3,3-pentafluoropropene) and 4 mass % of HFC32 (difluoromethane).

TABLE 1 EXAM- EXAM- EXAM- EXAM- EXAM- EXAM- EXAMPLE PLE 1 PLE 2 PLE 3PLE 4 PLE 5 PLE 6 7 EXAMPLE 8 CONTENTS BASE OIL A1 — — — — — — — — (MASS%) A2 — — — — — 90.1 93.1 94.1 A3 89.6 92.6 93.6 94.1 94.4 — — —ADDITIVE B1 — — — — — 1.0 1.0 1.0 B2 1.0 1.0 1.0 1.0 1.0 — — — B3 1.21.2 1.2 1.2 1.2 1.2 1.2 1.2 C1 1.5 1.5 1.5 1.5 1.5 1.0 1.0 1.0 C2 — — —— — — — — C3 — — — — — — — — D1 5.0 2.0 1.0 0.5 0.2 5.0 2.0 1.0 E1 0.50.5 0.5 0.5 0.5 0.5 0.5 0.5 F1 1.2 1.2 1.2 1.2 1.2 — — — F2 — — — — — —— — F3 — — — — — 1.2 1.2 1.2 TOTAL 100 100 100 100 100 100 100 100SEALED TUBE TEST OIL GOOD GOOD GOOD GOOD PALE GOOD GOOD GOOD APPEARANCEYELLOW CATALYST Cu Cu Cu Cu Cu Cu Cu Cu APPEARANCE COLOR COLOR COLORCOLOR COLOR COLOR COLOR COLOR CHANGE CHANGE CHANGE CHANGE CHANGE CHANGECHANGE CHANGE SLUDGE NONE NONE NONE NONE NONE NONE NONE NONE GENERATIONEXAMPLE EXAMPLE EXAMPLE EXAMPLE EXAMPLE EXAMPLE 9 10 11 12 13 14 EXAMPLE15 CONTENTS BASE OIL A1 — — 91.1 94.1 95.1 95.6 95.9 (MASS %) A2 94.694.9 — — — — — A3 — — — — — — — ADDITIVE B1 1.0 1.0 — — — — — B2 — — — —— — — B3 1.2 1.2 1.2 1.2 1.2 1.2 1.2 C1 1.0 1.0 1.0 1.0 1.0 1.0 1.0 C2 —— — — — — — C3 — — — — — — — D1 0.5 0.2 5.0 2.0 1.0 0.5 0.2 E1 0.5 0.50.5 0.5 0.5 0.5 0.5 F1 — — — — — — — F2 — — — — — — — F3 1.2 1.2 1.2 1.21.2 1.2 1.2 TOTAL 100 100 100 100 100 100 100 SEALED TUBE TEST OIL GOODPALE GOOD GOOD GOOD GOOD PALE APPEARANCE YELLOW YELLOW CATALYST Cu Cu CuCu Cu Cu Cu APPEARANCE COLOR COLOR COLOR COLOR COLOR COLOR COLOR CHANGECHANGE CHANGE CHANGE CHANGE CHANGE CHANGE SLUDGE NONE NONE NONE NONENONE NONE NONE GENERATION

TABLE 2 COM- COM- COM- COM- COM- COM- COM- COM- COM- PAR- PAR- PAR- PAR-PAR- PAR- PAR- PAR- PAR- ATIVE ATIVE ATIVE ATIVE ATIVE ATIVE ATIVE ATIVEATIVE 1 2 3 4 5 6 7 8 9 CONTENTS BASE OIL A1 100 — — — — 96.1 — — 96.4(MASS %) A2 — 100 — — 95.1 — — 96.1 — A3 — — 100 94.6 — — 95.7 — —ADDITIVE B1 — — — — 1.0 — — 1 — B2 — — — 1.0 — — 0.3 — — B3 — — — 1.21.2 1.2 0.9 1.2 1.2 C1 — — — 1.5 1.0 1.0 — — — C2 — — — — — — — — 0.7 C3— — — — — — 1.5 — — D1 — — — — — — — — — E1 — — — 0.5 0.5 0.5 0.5 0.50.5 F1 — — — 1.2 — — 1 — — F2 — — — — — — 0.1 — — F3 — — — — 1.2 1.2 —1.2 1.2 TOTAL 100 100 100 100 100 100 100 100 100 SEALED TUBE TEST OILBLACK BLACK BLACK DARK YELLOW PALE BROWN YELLOW PALE APPEARANCE YELLOWBROWN BROWN CATALYST Fe Fe Fe Cu Cu Cu Fe Cu Al Fe Cu Cu APPEARANCEBLACK BLACK BLACK COLOR COLOR COLOR COLOR COLOR COLOR Al Cu Al Cu Al CuCHANGE CHANGE CHANGE CHANGE CHANGE CHANGE COLOR COLOR COLOR SLUDGELITTLE LITTLE LITTLE NONE NONE NONE NONE NONE NONE GENERATION

TABLE 3 EXAMPLE EXAMPLE EXAMPLE EXAMPLE COMPARATIVE 16 17 18 19 10CONTENTS BASE A3 96.3 94.8 91.3 89.8 96.8 (MASS %) OIL ADDITIVE B2 0.30.3 0.3 0.3 0.3 B3 0.9 0.9 0.9 0.9 0.9 C3 1.5 1.5 1.5 1.5 1.5 C4 — — 5.05.0 — D2 0.5 2.0 0.5 2.0 — E1 0.5 0.5 0.5 0.5 0.5 TOTAL 100 100 100 100100 SEALED TUBE TEST OIL YELLOW YELLOW YELLOW YELLOW YELLOW APPEARANCECATALYST GOOD GOOD GOOD GOOD GOOD APPEARANCE SLUDGE NONE NONE NONE NONENONE GENERATION ACID VALUE (mgKOH/g) 0.29 0.17 0.06 0.11 0.45

Remarks

All of the base oil used was polyalkylene glycol polymer (PAG), whichwill be specifically shown below.

A1: Me-PO/EO-Me (polyoxypropylene polyoxyethylene copolymer dimethylether, a molar ratio of PO/EO 9:1), kinematic viscosity at 40 degrees C.44.5 mm²/s, kinematic viscosity at 100 degrees C. 10.0 mm²/s

A2: Me-PO-Me: polypropylene glycol dimethyl ether, kinematic viscosityat 40 degrees C.: 50.7 mm²/s, kinematic viscosity at 100 degrees C.:10.8 mm²/s

A3: Me-PO-Me: polypropylene glycol dimethyl ether, kinematic viscosityat 40 degrees C.: 44.0 mm²/s, kinematic viscosity at 100 degrees C.: 9.6mm²/s

Additives added to base oil are as follows.

Phosphate Extreme Pressure Agent

B1: B1: dioleyl hydrogen phosphite (amount of phosphorous: 5.34 mass %)

B2: tris(nonylphenyl)phosphite

B3: TCP (tricresyl phosphate)

Epoxy Acid Scavenger

C1: α-olefin epoxide (C-12, 14)

C2: 3,4-diepoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate

C3: α-olefin epoxide (C-16)

C4: PPG-DGE (polypropylene glycol glycidyl ether)

Unsaturated Organic Compound

D1: α-farnesene

D2: 1-hexadecene (C₁₆H₃₂)

Antioxidant

E1: DBPC (2,6-di-tert-butyl-4-methylphenol)

Other Additives

F1: oleic acid potassium

F2: N-dialkyl amino methyl benzotriazole

F3: sorbitan monooleate

Evaluation Result

Examples 1 to 15 shown in Table 1 are results of sealed test tube testsin which lubricating oil composition containing α-farnesene (unsaturatedorganic compound) is mixed with a refrigerant. In this case, appearancesof the compositions were normal, and colors of the catalysts did notchange except that of Cu. Sludge was not generated. Comparatives shownin Table 2 are arrangements solely consisting of base oil. Comparatives4 to 9, which had the same composition arrangements as the Examplesexcept that α-farnesene was not added, showed notable deterioration inthe appearances of the compositions and the catalysts in the sealed tubetests. It was also known that the presence of the extreme pressure agentor the acid scavenger did not show a noteworthy effect other thanprevention of sludge generation.

Examples 16 to 19 in Table 3 show results of autoclave tests in whichlubricating oil composition containing 1-hexadecene (unsaturated organiccompound) was mixed with a refrigerant. In all of the arrangements,appearances of the compositions were substantially normal, and colors ofthe catalysts showed no change. Comparative 10 had the same compositionarrangements as Examples 16 and 17 except that 1-hexadecene was notadded in Comparative 10. In the autoclave test conducted with such anarrangement, appearances of the composition was substantially normal,and colors of the catalysts did not show change. However, it was knownfrom the great increase in the acid value that the base oil was greatlydeteriorated by reacting with oxygen.

It can be concluded from the results set forth above that thelubricating oil composition for refrigerator to which an unsaturatedorganic compound is added according to the invention can be stably usedfor a long time in the presence of oxygen.

INDUSTRIAL APPLICABILITY

The present invention can provide a lubricating oil composition forrefrigerator with excellent stability even when a refrigerant having anunstable structure such as unsaturated fluorohydrocarbon compound isused.

1. A lubricating oil composition for a refrigerator, comprising: a baseoil; and an additive added to the base oil, wherein the additive is anorganic compound comprising a double bond in a molecule of the organiccompound.
 2. The lubricating oil composition for a refrigeratoraccording to claim 1, wherein the organic compound is an unsaturatedaliphatic compound.
 3. The lubricating oil composition for arefrigerator according to claim 2, wherein the unsaturated aliphaticcompound is α-olefin.
 4. The lubricating oil composition for arefrigerator according to claim 2, wherein the unsaturated aliphaticcompound comprises a conjugated double bond.
 5. The lubricating oilcomposition for a refrigerator according to claim 1, wherein the organiccompound is a compound selected from the group consisting of terpenesthat comprise a double bond.
 6. A refrigerant, comprising thelubricating oil composition for a refrigerator according to claim 1,wherein the refrigerant comprises: at least one of fluorine-containingorganic compounds selected from the group consisting of compoundsrepresented by following molecular formula (A); or a combination offluorine-containing organic compound and saturated fluorohydrocarboncompound,C_(p)O_(q)F_(r)R^(s)  (A) where: R represents a Cl, Br, I or hydrogenatom, p is an integer in a range of 1 to 6, q is an integer in a rangeof 0 to 2, r is an integer in a range of 1 to 14, and s is an integer ina range of 0 to 13; and if q is 0, p is in a range of 2 to 6, and themolecule comprises at least one carbon-carbon unsaturated bond.
 7. Therefrigerant according to claim 6, wherein the compound represented bythe molecular formula (A) is a compound represented by at least one ofmolecular formulae C₃HF₅, C₃H₂F₄, and C₃H₃F₃.
 8. The lubricating oilcomposition for a refrigerator according to claim 1, wherein the baseoil is at least one of mineral oil and synthetic base oil, and thesynthetic base oil is at least one compound selected from the groupconsisting of alkyl benzene, alkyl naphthalene, poly-α-olefin, polyvinylether, polyalkylene glycol, polycarbonate, polyol ester and anether-base compound represented by formula (1)Ra-[(ORb)n—(B)—(ORc)k]_(x)-Rd  (1)  where: Ra and Rd each represent ahydrogen atom, an alkyl group having 1 to 10 carbon atoms, an acyl grouphaving 2 to 10 carbon atoms or a hydrocarbon group having 2 to 6 bondingsites and 1 to 10 carbon atoms; Rb and Rc each represent an alkylenegroup having 2 to 4 carbon atoms; n and k each represent an integer in arange of 0 to 20; x represents an integer in a range of 1 to 6; (B)represents a polymerization site comprising 3 or more monomer units eachrepresented by formula (2)

 where: R⁴, R⁵ and R⁶ each represent a hydrogen atom or a hydrocarbongroup having 1 to 8 carbon atoms, R⁴, R⁵ and R⁶ being allowed to bemutually the same or different; R⁷ represents a divalent hydrocarbongroup having 1 to 10 carbon atoms or divalent ether-bondedoxygen-containing hydrocarbon group having 2 to 20 carbon atoms; R⁸represents a hydrogen atom, a hydrocarbon group having 1 to 20 carbonatoms; m represents a number whose average value is in a range of 0 to10; when m is plural, plural m are mutually the same or different pereach unit; R⁴ to R⁸ each are mutually the same or different per eachunit; when R⁷O is plural, plural R⁷O are mutually the same or different;and when both k and n in the formula (1) are 0, m is an integer of 1 orlarger in the formula (2).
 9. The lubricating oil composition for arefrigerator according to claim 1, wherein the base oil is further addedwith at least one additive selected from the group consisting of anextreme pressure agent, an oiliness agent, an antioxidant, an acidscavenger, a metal deactivator and an antifoaming agent.
 10. Thelubricating oil composition for a refrigerator according to claim 1,wherein a slide portion of the refrigerator comprises a, engineeringplastic, an organic coating layer, or an inorganic coating layer. 11.The lubricating oil composition for a refrigerator according to claim10, wherein the organic coating layer is a coating layer ofpolytetrafluoroethylene, a coating layer of polyimide, a coating layerof polyamide-imide or a thermosetting insulating layer comprising aresin paint comprising a resin base material comprising polyhydroxyetherresin and polysulfone-base resin; and a cross-linker.
 12. Thelubricating oil composition for a refrigerator according to claim 10,wherein the inorganic coating layer is a graphite layer, a diamond-likecarbon layer, a tin layer, a chromium layer, a nickel layer, or amolybdenum layer.
 13. A heating/cooling system comprising thelubricating oil composition for a refrigerator according to claim
 1. 14.The system according to claim 13, wherein a water content within thesystem is 500 ppm by mass or less while a residual air partial pressureis 13 kPa or less.